1. Field of the Invention:
This invention relates to an electronic computer, and more particularly to an electronic computer such as a portable electronic calculator having a display.
2. Description of the Prior Art:
FIG. 10 shows a conventional portable electronic calculator. The calculator of FIG. 10 comprises a liquid crystal display (LCD) 51, a fraction entry key 52, numeric keys 53 for entering numbers, an equal [=] key 54, and an [a/b] key 55 for converting a mixed fraction to an improper fraction or vice versa. The LCD 51 comprises a main display area 51a, and a fraction display section 51b which includes a numerator display area 51c and a denominator display area 51d. When a fraction is to be displayed on the LCD 51, the numerator and denominator of the fraction are displayed on the numerator display area 51c and the denominator display area 51d, respectively. In the case of displaying a mixed fraction, the integral part of the mixed fraction is displayed on the main display area 51a.
In the calculator of FIG. 10, a fraction can be input in the following manner. First, the numerator is entered using the numeric keys 53, and then the fraction entry key 52 is pressed to determine the entry of the numerator (rows A and C in FIG. 11). Next, the denominator is entered, and when the [=] key 54 or another key is pressed, the entry of the denominator is determined while the resulting fraction is reduced to the lowest term if reducible (rows B and D in FIG. 11). When the [a/b] key 55 is pressed, the conversion from an improper fraction to a mixed fraction or vice versa is conducted (row E in FIG. 11).
In a conventional calculator, as can be seen from rows B and E in FIG. 11, a fraction is displayed with both the numerator and denominator aligned to the right. When there is a difference between the number of digits of the numerator and that of the denominator, therefore, the numerator or the denominator, whichever smaller, looks squeezed to the right on the display as compared with the other, making it difficult for the operator to quickly and correctly recognize the displayed fraction. In particular, this problem becomes more serious when there is a great difference between the number of digits of the numerator and that of the denominator.
FIG. 12 shows other examples of key operations for inputting fractions and their displayed results. As shown in rows B and D in FIG. 12, in the case of displaying a mixed fraction, the numerator and denominator of the fraction as well as the integral part thereof are right-justified on the LCD 51. This leaves blank space between the integral part and fractional part of the mixed fraction displayed on the LCD 51, making it difficult for the operator to quickly and correctly recognize the mixed fraction on the display.
On the other hand, in a portable electronic calculator, calculation results are sometimes obtained and displayed in exponential notation mainly because of a limit to the maximum number of digits available for arithmetical calculations within the calculator. To display a number, obtained as a result of an arithmetical calculation, etc., in exponential notation, a conventional calculator has a display such as shown in FIG. 13. The display of FIG. 13 includes a mantissa display section 151 for displaying the mantissa of the number and an exponent display section 152 for displaying the exponent of the number.
FIG. 14 shows examples of key operations on a calculator equipped with the display of FIG. 13 and their displayed results. Rows A to C in FIG. 14 show a sequence for entering a number 1.234567891*10.sup.99. First, the mantissa (1.234567891) is entered (row A in FIG. 14). In this state, the entered mantissa is displayed on the mantissa display section 151, but since the exponent is not entered yet, nothing is displayed on the exponent display section 152. Next, when an "EXP" key is pressed, the entry of an exponent is enabled, the enabled state being indicated by "00" on the exponent display section 152 (row B in FIG. 14). Row C in FIG. 14 shows that the entered exponent (99) is displayed on the exponent display section 152. Row D in FIG. 14 shows a sequence for calculating .sqroot.2 (the square root of 2). Since no exponent results from the calculation, the exponent display section 152 displays nothing. Row E in FIG. 14 shows a sequence for calculating 69? (the factorial of 69). The calculation result shows 1.711224524*10.sup.98. As shown in row E in FIG. 14, the mantissa of the result, "1.711224524", is displayed on the mantissa display section 151, while the exponent "98" is shown on the exponent display section 152.
As described above, a conventional calculator has a dedicated display section for displaying the exponent of a number expressed in exponential notation. On the other hand, in the field of calculators, it is desirable that fractions be displayed in a format closer to the usual representation in order to enhance operability. If a conventional calculator is to be further equipped with a display section for displaying a fraction, however, the problem is that the entire display will become complicated and expensive in construction.